Two-way signal transmission system



Sept; 943. N. w. BRYANT 2,328,951

TWO-WAY SIGNAL TRANSMISSION SYSTEM Filed July 17, 1942 2 Sheets-Sheet 1FIG. I

WL 2 EL COMP 4)0 .39 1/ f /3 l/L/ 714 $2 /0 F161 2 E I AMP I AvflvA'Av V5: 20 l w 5 AMP AMP a A I L AMP /N VENTOR NWBRm/VT aZCfM A T TORNEV p1943- N. w. BRYANT 2,328,951

TWO-WAY SIGNAL TRANSMISSION SYSTEM Filed July 17, 1942 2 Sheets-Sheet 2INVE/V TOR N "(BRYANT Brim-25W 4 ATTORNEV The inventiofi rglqt gg tctvgg way signal transmiissionsystems and particularly to (iilcuigs ig l;

; 2km purpbs' OI: enablin propel li zymzase k mqmmm anintexmeaiatetzansa p smlttirgg Q15. WW

l-am ssa q m mmsd) I ioq will be un'cier'st'ObdT-rbmth fbl'lqwing tameddescription wher gggfig conjunction with hgetd in shunt with tholipgsoc-tio be't we se ries' resistors? ye backard-ac by. echoes;Howevemsime ythei ex ndfi get! through mthoutrattenuaati'omonlyoatstimqsl when; theyare;maskedqwmheibneakingsignailsi i A mthe signalvolume levebof thbrea-lqng parjzyi the: volume oi the! fdnmers signahiatthe; outp of his own compressomwifl be lowenthani nonnalo The signal ofthe breaking partysam-thevinput ofi mnm trgmsmrmw Zfixmhalving anon-41mm; im-isms:

be: a; cophermox dmr ectiml mama; b "as E21 ,4

xresistonlfi': and: ausim-iiannm-Jimaa: J2; Shh-Mada: mama 11mm msis qni2%.; msxm ml oonnaehedmzsemies wibmnashwsiqm 05 mg; and

linegr; ne'sistomot meal: alum: shunting; tho; 3%;

1 hiswexpandenwill alsobe lower: than nor-man and hhoamiotsinsestthenproper amountof-n gaimim his expander; I'hereiore; while he isxalblgto bneak through, the volumesofi his signals-reachathe 'othemparty willbelowe r: than normaliby arr-amount approximately equa h p9; the-d-ifieseno i-mtwlkihg volumesx This; however, is n more his words wi flgetthrough at l normal they occu n du r ing the pauss of flheother-talker;

Any variation received v'olume isi rio'ii dis-tui'b mg to the lattertalkei=- because," ofl the: masking:-

for a talking patty to tmderstainda 4i bz oahing p'agtty whil-e theformer istalking h I: has been pomedwuu that .the' increose m notexcised (NE+-RL)'. Whenmisisg alowqglue;

the improvement; mayhofi. b sufl ib t; to 1 1151165 the use ofi suchdevices by themselvs -pzyaotigai1f-as echo suppressors pen Se. Toincyease this echo loss, on auxflianyeeho suppressor may be added as inthe modifications of: uhsimmmon mus identification characters; Thepatticulah 59m? i neiiudes in"the-outgoing path EA! hi on L ay into thepath by a n for this]compfess x irioluges gongw l0 having itsinputicohnectogl 'acfossit eluding ."hhehparallelv comiensem Ski 84351;wfi n m meamm -lizapoom thmprrmaicy-windin on tmoute brid es: haying;its inpmxmmxeotedgi tosthei out-,

out; or .Lampfiflen- 3:4;- anat; its: output-u cementethazoughhhebseries; diizectibmmristoz:

20, 2| of the compressox nominal; eimuih In across? the sama diagonaizoftheweofigfier bridgsllofimhe Qomnresson variofllosserzvhh A: hsngroxemcomthe cazess-jcontnol eircuit iz; v .mAn; auxiharm echo; suppressor,compr sesthe;

elexihiaxxmagnetioz relays-q 318;: having, its Ec me,1 'a,t1ngwinding-connected imgserieshwithone; side oh: the. cfosshcontrolicirwit: 5; between the rootifism 3i:

manneriwhiohwmilhbe dsemxbed below 'other diagonalof the bridge If! invario-lossei The volwne. iahge expanderi VEW incmdes inand aw preceding"varioL-lossep VLQ consisting" of ailoss; tpadw 33; comprisingthe, tandemcouneeted:

t-rxansfiormezs 4m amt-4 t: with cmsssd mner. ings, mathewrwnsmissionpgnhjm m irant at the; varifli-hlossezz andthe assopiatem resistom l3,

s ime-System01? Big; 2 opyexates as follows: n I :Ifif'iihfi; idlecondition; Ofi the: circuit; thatyig: WiEh'HOI SDBBGhXWaYQSbeingwqransmibted Outiovexi the; path and: no; speechmves being receivedommtho receivingpath Wmthoinner' windings closed: oontzmts: 0.1 the;rlay 38: T of; the auxiliary;

.stantialiyl moulrossiinltheuinpmgv ofi'the path: EA-.; With-no coxitxol1 cument: ap lied-Ito the: copper:

oxid regtifiersfimthe rectifier bridge; l1 from the associated;commesson' controhoiicuit: k: and the" orossmontrolt circumzi,thmefieotiveyshunt impedi'rice; ofqthekbmidgefi tFl'zis thafi the varioIosseiu' prom comparat wgly sma l lf loss j in th iaa --EA so-thpt'theeffe'qtive gam s-ms he mso, with no cosine; gu ken ma pueonio ik'gavmwmmu; the impedarioes of the series press'or thelbsfiiwalfis ofiwhibhpad in themathhA -vis controlled bwtho operation ofanelayi 18m, tho

eshocsnppnessor; so thatathe' pad flamsentsesuh coil"- Hwto the .line'WL overwhich they will be at the other station (not shown) alsoprovides a'rnaximum gain of 25 decibels'and a maximum loss of 25decibelsy'respectively, so thatthe overall n'et'gain in thefour-wirecircuit is zero.

. uissum'e 'that the west subscriber'is speaking.

flisf' 'speech current "received over the line WL will be impressedbyhybrid coil Hw on the input of tnepath -EA andwillpassthrough the losspad 39 -and the vario' -losser 'VLr with little atte'nua-r tiorrfto theinput of the amplifier Ill and will be amplified thereby" andtransmittedover the path 'EA' to the east stationJ- Aipor-tion of the amplifie'dwaves" intheoutput o'f amplifier l diverted into the compressor con'trolcircuit I will be amplified' by amplifier l8, rectified by the rectifieri9 and applied across the timing-network 20',2|

to theire'ctifierbridge. ll ofyario losser- VL1, to 1controltheim-pedances of {the rectifiers therein insuch' manner asto'increase the loss value of the vario-"losser-Vm in proportion to theincrease in applied rectifier current. .I'hewolume range of westfsiamplifiedtwaves thereafter transmitted out' over thepath EAwill'therefore be compressed ina'-givenratio (2' to 1 inthe workingrange).

The action-of the volume 'range expander in the"path EA at the 'eaststation' (not shown) will be desc'ribed by reference to the identicalexpander VEw'linthe output otthe path WA at the west-statiohillu'strated; for the case where speech:

currents from ian eastsubscriber are being received over'th'e path'WA.

East's s'pe'ech Waves with the icompression in volume range produced bythe compressor in thepath WA atgthe east station (not shown);corresponding to the compressor in the path EA at thiwest station,'-onarriving at the weststation, will' be divided between'the maintransmission path and the common input to the expander cohtrolicircuit 3and the cross-control circuit 5. The portion of eastsspech wavestransmitted intothe expander control circuit 4 willbe amplifled by theamplifier 30- and rectified bythe rectifier 3| therein an'd will beapplied through the timingnetwdrkl32g33 to the vario losser. VLe by theI connectionsto the ini'd taps of the shunt resistor 29 and'oftheprimary winding of output transformer .24' therein; The appliedrectified currents willfiow through the series rectifiers 25 and" 2] inthe vario-losser VLz in the direction iniswhichTthey-are-pointed so thattheir series resistance-is decreased by anamount (25 decibels)i.*equalto the loss'introduced in eastsspeech- Waves by the,..compressor at theeast station:-

Thus the main :portion of-leasts speech waves passing throughthe varioloss'erfVLz andamplified bytheamplifier 22 in the output of'the path 7WA areeffectively expanded in the .same degree as 1 they: are.compressed atthe east terminal. These waves are thenpassed through thehybrid transmitted tothe west subscriber.

:Anotherfportion of eas'tfs speech waves in the input of thevario-losser Vlein path :WA are divertedinto'the cross-control circuit"and are amplified by the amplifier 34 and rectified by therectifier-:35 therein. As the latter, rectifier isconnectedin parallel.withtherectifier l9and the timing network 20,, 2! of the compressorcontrol circuit tacross the same diagonal of the rectifier bridge H-in;vario-1osserVL1,' therectified ourin thepathEA being equal to theeffective gain inserted bythe volume expanderVEw in response to. eastsincoming signals in the path WA, and operateszto produce a correspondingsuppression of the echoes of .ea'sts signals reflected into the input-ofpath EA.: As pointed out previously in connection with Fig. 1 themaximum value of this echo loss is limited to. (NL+RL), i. e., half thecompanding range, or about 25 decibels for'th particular compandor used.

- Hang-over condenser 31, which is connected across the rectifier 35 ofthe cross-control circuit 5,"provides a means for holding the lossinserted in jthe'path EA by the cross-control circuit, long enoughtogattenuate echoe returning from, the

circuit connected to the four-Wire circuit.

The condenser 31 is'charged whenever the cross-- controlo-perates toinsertloss in the compressor: VCw, and prolongs theaction after thesignal at. the input-to the cross-control circuit 5 has passed.;, In.order to prevent this hang-over .condenser.

from :afiectingthe; attack and recovery times of the-regular compressorcontrol circuit '4, it is isolated 'frorm-theirectifier E9 of the lattercontrol circuit by the directional vvaristor 38, which may'consist or anumber ofc'opper-"o-xide rectifier discs'; The length of the-hang-overis determined-by the time constant of the network comprising condenser31,*theiso1ating varistor '36;

the .rectifiers 35. :19 of the? two controls, the resistance-condensernetwork connecting these two controls to thecompressor rectifier bridgell, andthe-;rectifier-bridge H itself. q

;'I he result of connecting the cross-control cir'- cuit 5-and thecompressor control circuit. 4 to- 1 gether is to. give the controlcircuit ,With the larger output control of the compressor VCw, exceptwhen the two outputs are approximately equal, at which point bothcontrol circuits take partial control. Thisactionmakes break-in easysince 'atalker trying to breakcan take control of the compressor at hisendof the circuit, if hetalks as-loudly as the other party, making theaction; of that compressor the same as if the other party were nottalking. Thus the volume at theoutput of the compressor and thereforeat; the input to'expander v(in the breaking path) is normal. This meansthat the expander will fully compensate for the loss in the compressorand; the received volume will be normal. Even if the breaking party doenot speak-loudly enough 1 to-take control of thecompressor at his end ofoutput of. rectifier 35 inthe cross-control circuit 5 whenever thatcross-control circuit is operated the line he will still be heard at thereceiving.

end. but ata lower volume.

he additional echo-loss required to make the system of Fig. 2 practicalas an echosuppressor is provided by the auxiliary suppressor.comprisingtherelay 38 andthe loss pad 39 and associated linearresistoriz. The relay 38 is operatively energized by the rectifiedcurrent in the by incoming speech; currents. Theoperation of relay 38 toopen its contacts opens the normal short-circuitia round the resistor 42connecting that resistor effectively in series with the innercross-connected windings oft-he'transformers 40-v and..,4l in losspad 39so as-to increase theloss rentsofthe cross-controlcircuit 5 operateinsimilar manner. as the rectified currents of the compressor controlcircuit I, described above, to effectively increase the loss value ofthe variolosserillminthelpathEe, 1 0 thus i serted the input ofthe pathEA'by the value of that The amount of loss inserted by the auxiliary Isuppressor cannot'be made large without seriously affecting thebreak-inc The volume of the breaking party is reduced by the lossinserted. In addition, the breaking signal, when iteperates A -nect'ed"coils in "loss pad 19 to connect them in series-aiding condition inwhich the padprovides minimum-loss inthe path EA; I

When west stops talking or pauses so o'f the compressor control circuit44', the condenser ll discharges through the varistor 48 and theresistor49,-resistor5i] and V113, the discharge time of this circuit beingapproximately the sameas the i'ecovery 'time of the=compressor= VCWi.f'Under this condition; condenser 82 also "dischargesreducing thepositive bias on the control grid of the tube 12 so that the (DIFF) re--1ay-.'M:in =its output releases. t-- i master d s gnal jollo z o ed byreceived signal If whilena transmitted signal is present and the circuitof Fig. 3 is ingthe transmitting con- 1 dition;-asignalfrom theeastsubscriber is received over; the incoming path WA, the portion ofgthissignal entering the expander'controlcir- Jcuit 53 and the cross-controlcircuit 62 will producegvoltages-across the condenser 51 at thev,outputof the expander-rectifier 55 and across the; condenser 65 at theoutput of the cross-controlrectifier 53,, The voltage across condenser51 ;.will cause biasing. direct current .to flow throughthe directionalvaristor 58 and theresistor 59 to,the expander vario-losser VL4-in Vsuch direction as to, reduce the impedance of its series varistorsandthus to reduce the losszin the path WA toeasts incoming signals,thereby ,ef-

fectively expanding, the volumerange of the latter. f. s i Thevoltageproduced across thecrossecontrol circuit condenser 85,,if.sufficient, causes current that-thetransmitted signal is removed fromthe input If whileithe received signal from east is still present weststransmitted signals terminate, the voltage drop (TCV).produced'betweenpoints H .and Grim the cross-control circuit 62decreases tozero. and the circuit functions as it would if notransmitted signal had been present.

Ifthe signals received-from east terminate while the signals transmittedby west are still 5 flow from Etc F-throughthe resistor .66 and v thedirectional varistor 61, charging "condenser lfipa nd then-fromli toGthrough: directional .v aristor 68 and resistor 69,-.to the rectifierbridge 5| of the compressorpvario losserV113;- '(When the voltageproduee d across the compressor losser bridgetl *bythe compressorcontrol circuit ljinrresponseto wests transmitted signals i is. greater:than (the voltage "produc'ed' across con- .densr 65in the-cross--controlcircuit BZ by the -signals'receivedfrom east, nosteady-statecur- .:.rent will flow from E to G- in the cross-control .circuitiIGZ.).-.-'Ihevoltage-produced between E and .F .bias'es. the control 'grid ofthe tube H positively. andg whensufficient, increases the ;.platecurrent of that tube. to a point where the -relaylchain'comprisin grelays 13' and 18 operates. The operation of these relays does not causethe blockingof the transmitting'circuit EA'by the present the voltagedrop (RCV) produced between F and G in the cross-control circuit 62 willgradually decay andthe (DIFF) relay 14 will'reoperate. The (SUP) relayl3. and the relay 18 after its hang-over period will also release. Whichoccurs first will depend on the relative amplitudes of the transmittedand received signals. In either case, the suppression provided by thevariable loss pad i9 is removed from the transmittingcircuit EA.

Received signal only; The signals received overtheincoming path WA fromthe east subscriber will pass through the fixed loss pad 84,variorlosser VLi, amplifier 52 andhybrid coil Hw to the line LW overwhich n they will be transmitted to the west subscriber.

A portion of these signals will be diverted from the path WA afterpassing through the fixed loss pad 84, into the common input of theexpander control circuit 53 and of the cross-control circuit 62, andwill be amplified by the common 1 amplifier 54 therein. The portion ofthe amplisea waves passing through the transformer 56 .willbe rectifiedby the expander-rectifier 55 and will produce a voltage acrosscondenser5'l. This will cause biasing current to fiowthrough directionalvaristor 58 and resistor 59 to the variolosser VI in suclrdirection asto reduce the impedance of the series varistors therein and thuseffectively expand the volume range of easts signals passing throughthat vario-losser.

- through the transformer (to the cross-control .suppre'ss'or co'il pad19 because the (DIFF) relay -i4'in -the outputof tube 12 is stilloperated holdingithat padin the low loss condition. When the-voltagedropproduced 'between F and Gby uthe-cross-controlcurrentis'equal to thevoltagedmpbtween. H. and Gr dueto the-compressor r 1 controlcurrent theplate current of; the tube 12 decreases toa point'where the (DI-FE)relay "M releases at which' time the short-circuiting connection acrossthe inner windings ofthe suppressor coils of pad- 19 are opened toconnect these windings in series-opposing relation; providingka'blocking loss in the transmitting circuit "EA. "The"blocking-ofthecircuit EA in this man-- her is considerably-slower than when there isno-transmitted signal and theiDIFF) relay [4 'is not'joper'atedi "Untilthe latter relay releases, tra'nsmitted speech can pass out over thepath to-th east statiomand will mask any initial rectifier 63 and willbe rectified thereby to produce avoltageacross the condenser 65. This wllcause current to fiow from E to F'charging condenser I0, and then fromF to G and to the rectifierbridge 5| in the compressor vario-losser VLacausing the latter to insert a loss in the path JEAN Thevoltage producedbetween E and -E.1n .the control circuit biases the control grid ,7 ofthe tube ll positively, increasing. the plate current of that tube,.current is sufilcient, the suppressor relay chain If, the increase inplate 13, 18, will be-operated to open the circuit of .the suppressorcoil loss device 19- to blockv thetransmitting path EA. When the signalreceived ,from east is a few decibels or more above the marginal valuerequired, to operate tube H, the

- echo suppressoris operated in less than 3 milliseconds. This fastoperation is necessary in any receiving .type of suppressor in. order tosuppress echoes properly.

1 ;';The voltage drop'produced between and I u The 1;other..portion:ofthe amplified waves will pass 'ee 5. I

Will ey ieiete jerbs'e smart-i t mused-to t e w a1 OverfinterVubY thehemmed e: -3,"tIferecitmersfhiithndg"Gamay he f'ed that interval vanstorwe, we aascrfiwa ymmn mew-mm 'theism ana s"ec 'e *o the: im/(attain mumaware m smuae etion ebress the *suisprssei in said receiving preventingthe loss from affecting the input w 75 channel to reduce the loss valueof said seconq mm wev-er, mmmameam Kine s siemwantm@emm; m "the isystemMervin-mixer asingle 'transiomer 150mm yariorlosser in proportion, tothezamplitude, level of said incominig signals: saidcross-LcontroI'cirvcuit comprises: a thirdfrectifier control circuithaving its input connected to. said receiVinnhannel and itsoutput-connected'lto the vario-losser I of said compressing meansiin thesame manner as'the first rectifier control circuit thereior conetrolled-from said transmitting channel,v said auxv -iliary means"include ,a variablezloss ,padoi nor- 7 mallow loss value connected insaid transmitting channel, and relay means responsive'to the .rec-

..-tified waves insaid cross-contrclrircuit; to increase thellossvaluecf said rvariablewloss pad to said fixed amount; saidcrosscontrol;c ircuit includinga oneway transmissiondevice connectedbetween said relay means and-said first rectifier control circuit ofsaidcompressing means; to, prevent false operation of said; relay means inre.- sponseto outgoing signals in said transmitting channel. r

' 5. The terminal ofclairn linjwhichlsaid-auxil iary means is operatedbyth e voltage drop produced ina portionof said cross-,controlcircuitresponse to said incoming signalsand said other means includesmeans for]producing an oppcsing greater voltage dropin saidcross-controlcirinfitting' channel'fo'r a given hang-over time intervalafter thesignal' input to said cross-control circuit ceases. Q 1 1' 7.The terminal of claim 3 in whichsaidauxiliarynieans comprises avariablefloss. pad normany of low loss value, in saidtransmittingfchangnel beyond the outputof said compressing" means, andrelay means responsive to the voltage drop produced in a'po rtion ofsaid cross-control circuit by applied incoming signals to. increasetheloss value of said'p'adtosaid fixeda'mounfland said other means includesmeans foreffe'ctively disabling said relay means when the signal'oiitputof said compressing means exceedsjt'he: signal input to said'ex'pandingmeans by a given amount. f f ,1 ,1 V ,8. The terminal of claim 3, inwhichsaidco-mpressing means comprises a .vario-lossr of, nor l mal lowloss value insaid. transmitting channel, and a rectifier-"controlcircuit responsive to out? going signals in the output ofsaidvario-losser forincreasing the loss value of said'fvarioelosser inproportion to the amplitude level of "said outgoing signals, saidcross-control circuit comprises a second rectifier controlcircuitrespdnsivlto the incoming signals insaid receiving channelin front ofsaid expanding means,of suificient, level to operate thelatter, in theabsence of'outgoing signals of greater. level 'in 'theoiitpflt '0f,'sa'id vario-losser, to, increase thei'lossyalue' of said vario-losserby'an amount equal to the increase ingain of said expandingmeansinfresponseto said incoming signals, said auxiliarymeanscomprisesrelay means which when operatedinserts a loss of saidfixed amountlin saidtransmitting channel, an electron discharge deviceresponsive to a voltage drop produced in a portion; orJsaid secondrectifier controlcircuit byincoming signals ofZsaid sufiicient level, tocause the opera tlon of said relay means, and' neans iorinainltainingsaid loss of fixed amount in saidtranse a ance v l au e whe e out i ss..-

nals applied to said first rectifier control circuit areof higher levelthan the incoming signals applied to said second rectifier controlcircuit, and a second relay means responsive to opera tion of saidsecond electron discharge device for disabling 'the first relay meansand-said hang- 9. The terminal of claim 1 in which said compressingmeansincludes a vario-losser insaid transmitting channel, and a backward-acting control circuit controlling its loss value; in acicordancegyviththe amplitude le velof the out;

going signals in the output of said vario losser the output of saidcross-control circuit alsocontroll-ingthe loss value of saidvario losserinthe same manner as said backward-acting control circuit, in responseto the incoming signals in the in- P f pand a ean n dJQ iY n channel,said backward-acting control circuit and said crosscontrol circuitincluding individual re.- sistors connected in opposition, respectivelytraversed by the control currentto said vario-losser due to, saidoutgoing signals and due to said incoming signals, and of suchrelative-values that the control circuit with the larger output obtainscontrol of said vario-losser except when the -tjilp I outputs areequalwhen each obtains partial control, said auxiliary means beingoperatively responsive to thevoltage drop produced insaid cross-controlcircuit by :the incoming signals when their level ise qual' toor greaterthan the levelof the outgoing signals applied to said crosscontrolcircuit. Y f I} IOJ I n a two-'Way' signal transmission system includinga signalitransmitting path and a signal receiving path at each terminal,means in each Signal transmitting path controlled by outgoing signalsforvariably compressing their vol.- ume'range, means in'each signalreceiving path controlled by incomingsignals for variably expandingtheir volume range, a unilateral crosscontrol circuit at each terminalresponsive 'to in coming signals in the input of the. expanding means inthe signal-receiving path, in the, absence of outgoing signals'cfgreater. volumelevel in th output ofjthe compressing means in thetransmitting path. at' the. terminal, to control that compressing meansto-insert an echo suppres'sionloss of avalue dependent on thefvolumelevel of the controlling signals, in the signal transmitting path, and adifferential echo suppressor at each terminal controlled by the voltagesset up in the cross-control circuit by the incoming and outgoingsignals, to cause an additional fixed amount of suppressionloss to beinserted in the transmitting path when the volume level of the income'ing signals applied to thecross-control circuit is equal to or greaterthan the volume level of the outgoing signals in the output of thecompressing -means' in the signal transmitting path at the terminal.

Y 1 I NEWTON W. BRYANT',.E.

